AT&T MERLIN LEGEND Release 3.1 Maintenance And Troubleshooting Manual page 209

Trunk Errors
The CO fails to disconnect when the GS trunk is dropped by the
system.
After two occurrences, the trunk is put into a maintenance-busy state
and a permanent error is logged.
Loop-Start (LS) Trunk
No loop current exists when the LS trunk is seized. The port is marked
maintenance-busy , and a permanent error is logged after four occurrences.
Tie Trunk
The following events cause maintenance-busy on a tie trunk.
A seizure of an outgoing tie trunk fails.
A transient error is reported. After four unsuccessful seizure attempts,
the port is marked maintenance-busy and the error becomes
permanent.
The CO fails to disconnect.
A transient error is reported. After two occurrences, the port is marked
maintenance-busy and the error becomes permanent.
NOTE:
The test is not run on auto-out tie trunks.
Maintenance-Busy Programming
You can select
there is also a menu selection to include tie trunks.
Maintenance-Busy Status
See "Checking Ports" below for information on maintenance-busy status.
as a system programming option. If you do,
Central Office Problems
5–7